Ethylenediaminetriacetic acid (ED3A) and its salts (such as ED3ANa3) have applications in the field of chelating chemistry, and may be used as a starting material in the preparation of strong chelating polymers, oil soluble chelants, surfactants and others. Conventional routes for the synthesis of ethylenediaminetriacetic acid were achieved via its N-benzyl derivative, which was subsequently hydrolyzed in alkaline solutions to ED3ANa3, thus avoiding cyclization to its 2-oxo-1,4-piperazinediacetic acid (3 KP) derivative. One example of the synthesis of ethylenediamine-N,N,Nxe2x80x2-triacetic acid is disclosed in Chemical Abstracts 78, Vol. 71, page 451, no. 18369c, 1969. There it is stated that ethylenediamine reacts with ClH2CCO2H in a 1:3 molar ratio in basic solution at 10xc2x0 C. for 24 hours to form a mixture from which ethylenediamine-N,N,Nxe2x80x2-triacetic acid can be separated by complexing the same with Co(III). The resulting cobalt complexes can be isolated through ion exchange.
U.S. Pat. No. 5,250,728, the disclosure of which is hereby incorporated by reference, discloses a simple process for the synthesis of ED3A or its salts in high yield. Specifically, a salt of N,Nxe2x80x2-ethylenediaminediacetic acid (ED2AH2) is condensed with stoichiometric amounts, preferably slight molar excesses of, formaldehyde, at temperature between 0xc2x0 and 110xc2x0 C., preferably 0xc2x0 to 65xc2x0 C. and pH""s greater than 7.0 to form a stable 5-membered ring intermediate. The addition of a cyanide source, such as gaseous or liquid hydrogen cyanide, aqueous solutions of hydrogen cyanide or alkali metal cyanide, in stoichiometric amounts or in a slight molar excess, across this cyclic material at temperatures between 0xc2x0 and 110xc2x0 C., preferably between 0xc2x0 and 65xc2x0 C., forms ethylenediamine N,Nxe2x80x2-diacetic acid-Nxe2x80x2-cyanomethyl or salts thereof (mononitrile-diacid). The nitrile in aqueous solutions may be spontaneously cyclized in the presence of less than 3.0 moles base: mole ED2AH2, the base including alkali metal or alkaline earth metal hydroxides, to form 2-oxo-1,4-piperazinediacetic acid (3 KP) or salts thereof, which is the desired cyclic intermediate. In the presence of excess base, salts of ED3A are formed in excellent yield and purity. This patent also discloses an alternative embodiment in which the starting material is ED2AHaXb, where X is a base cation, e.g., an alkali or alkaline earth metal, a is 1 to 2, and b is 0 to 1 in aqueous solutions. The reaction mixture also can be acidified to ensure complete formation of carboxymethyl-2-oxopiperazine (the lactarn) prior to the reaction. Formaldehyde is added, essentially resulting in the hydroxymethyl derivative. Upon the addition of a cyanide source, 1-cyanomethyl-4-carboxymethyl-3-ketopiperazine (mononitrile monoacid) or a salt thereof is formed. In place of CH2O and a cyanide source, HOCH2CN, which is the reaction product of formaldehyde and cyanide, may also be employed in this method. Upon the addition of any suitable base or acid, this material may be hydrolyzed to 3 KP. The addition of a base will open this ring structure to form the salt of ED3A.
U.S. Pat. No. 5,284,972, the disclosure of which is hereby incorporated by reference, discloses N-acyl ED3A derivatives and a process for producing the same. The production of N-acyl derivatives of ethylenediaminetriacetic acid can be accomplished according to the following general reaction scheme: 
The starting ED3A derivative can be the acid itself, or suitable salts thereof, such as alkali metal and alkaline earth metal salts, preferably sodium or potassium salts.
Saturated N-Acyl ED3A derivatives that are the product of the foregoing reaction can be represented by the following chemical formula: 
wherein n is from 1 to 40. Where unsaturation occurs, the structure may be shown as follows: 
where n is from 2 to 40. As unsaturation increases, the formulae are: 
where n is 3 to 40; 
where n is 4 to 40; and 
where n is 5 to 40, etc.
Poly N-acyl ethylenediaminetriacetic acid derivatives, such as dicarboxylic acid derivatives having the following general formula also can be produced: 
where x is 1 to 40. Specific examples include mono and di ED3A derivatives such as oxalyldi ED3A, oxalylmono ED3A, maleylmono ED3A, maleyldi ED3A, succinoylmono ED3A, succinoyldi ED3A, etc.
Hair shampoos that are mild in terms of skin and eye irritation are desirable, especially for use on infant and children hair. xe2x80x9cNo more tearsxe2x80x9d Johnson and Johnson baby shampoo is an example of such a mild shampoo commercially available. However, such shampoos tend to be relatively ineffective in terms of lather formation, and are rather intolerant to water hardness.
The present inventors have found that N-acyl ED3A, when produced in pure form with impurities such as free fatty acids below about 1%, function surprisingly well as chelating surfactants, combining the properties of a chelating agent and a surfactant in one molecule. Detergent compositions containing N-acyl ED3A exhibit copious lather and cleansing properties and low ocular irritancy. Accordingly, these chelating surfactants can be advantageously used in detergent formulations including shampoos and skin cleansers.
It is therefore an objection of the present invention to provide novel detergent compositions comprising N-acyl ED3A.
It is a further object of the present invention to provide a mild shampoo that has acceptable lather formation, even in the presence of high water hardness.
It is a still further object of the present invention to provide a mild shampoo that causes minimal eye irritancy and low toxicity.
It is a further object of the present invention to provide a mild skin cleanser that has acceptable lather formation, minimal eye irritancy and low toxicity.
The problems of the prior art have been overcome by the instant invention, which provides a mild detergent formulation comprising N-acyl ED3A, preferably as the sodium or potassium salt. The acyl group is not particularly limited, and can include straight or branched aliphatic or aromatic groups containing from 1 to 40 carbon atoms, preferably from 8 to 18 carbon atoms.